Regarding Spam, the default usually is set as to not mark as read. Check this:

• Settings > Privacy & Security
• Scroll down to 'Spam' section

These are setting usually selected:

• Select 'When messages are marked as spam'
• Select : 'Move them to the accounts 'Spam' folder'

for 'Mark messages as read:'

• Do not select any of those checkboxes - uncheck if they are selected.
• Select checkbox: 'Enable adaptive spam filter logging'

You said you didn't change them, but check them anyway... There are two settings that affect that behavior. (In Windows):

- <Tools | Settings | General | Reading & Display |Automatically mark messages as read> . Here you can change the lag time or turn the feature off entirely;

- <Tools | Settings | Privacy & Security | Junk | Mark messages as read>.

I've checked my settings ad nauseam, since this started happening, out of the blue. It literally started happening all by itself one day, with no input from me, no software updates and no changes to my computer OS or anything else. Nothing has changed. I've unchecked and rechecked the desired settings, closed and reopened with old settings then new settings, but no change. I've even gone so far as to uninstall and reinstall Thunderbird (which is a painful process, due to having to set up my passwords and security permissions for all my email accounts, all over again), and I get the same results, over and over. This seems to be a glitch in Thunderbird. It happened once before, however it righted itself after a T-Bird firmware update. I've always update to latest version as soon as it's available, but it has not fixed it this time.

Using Bitdefender? I seem to recall it or its spam toolbar affected read status at one time.

No, I don't use Bitdefender. I don't know what that is.

How do you move it to trash? Seriously, you select the email and Thunderbird immediately marks the message as read, unless you mail provider marks it as such when they download it to your phone.

What does it's status really men anyway. It is no as if anyone but you knows what status your mail has. There are some urban myths out there suggesting that reading email somehow notifies the sender that mail has been read. That is a complete fallacy. Read detection is something that is done by stealth using images and tagged links, not bu sending some sort of read notification. SO why does it matter what your trash looks like?